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United States Patent |
5,207,535
|
Saab
|
May 4, 1993
|
Push-on gripper plate for use with rock bolts
Abstract
A push-on gripper plate for use in securement of a mesh screening means on
the protruding, threaded, end portion of a rock bolt inserted into a rock
face is disclosed. The gripper plate has a generally planar base portion
adapted to overlie the mesh screening means and a central opening in the
base portion having two or more leg portions positioned on the perimeter
of the opening and inclined upwardly, inwardly toward the center of said
opening above the plane of the base portion. A plurality of tab portions
are positioned on the perimeter of said opening in alternating arrangement
with said leg portions, the tab portions being inclined upwardly, inwardly
toward the center of the central opening above the plane defined by the
base portion.
Inventors:
|
Saab; Thomas L. (1390 Hazelton Blvd., Burlington, Ontario, CA)
|
Appl. No.:
|
785115 |
Filed:
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October 30, 1991 |
Current U.S. Class: |
405/259.1; 405/288; 411/533 |
Intern'l Class: |
E21D 011/00; E21D 021/00 |
Field of Search: |
405/302.3,288,259.1
411/437,526,527,512,533
|
References Cited
U.S. Patent Documents
2342910 | Feb., 1944 | Tinnerman | 411/525.
|
4740111 | Apr., 1988 | Gagnon | 405/302.
|
4784418 | Nov., 1988 | Pearson et al. | 411/525.
|
4911594 | Mar., 1990 | Fisher | 411/437.
|
Primary Examiner: Taylor; Dennis L.
Attorney, Agent or Firm: Hofbauer; Patrick J.
Claims
I claim:
1. A push-on gripper plate for use in securement of a mesh screening means
on the protruding, threaded, end portion of a rock bolt inserted into a
rock face, said gripper plate comprising:
a generally planar base portion adapted to overlie the mesh screening
means;
a central opening in the base portion having two or more leg portions
positioned on the perimeter of said opening and inclined downwardly,
inwardly toward the centre of said opening below the plane of the base
portion;
a plurality of tab portions positioned on the perimeter of said opening in
alternating arrangement with said leg portions, the tab portions being
inclined downwardly, inwardly toward the centre of said opening below the
plane defined by the base portion;
wherein the leg portions are dimensioned and otherwise adapted to
frictionally engage therebetween the threaded end of the rock bolt to hold
the gripper plate on the end of the rock bolt over the mesh screening
means.
2. A gripper plate according to claim 1, wherein the inclination angle of
tab portions is steeper than the inclination angle of the leg portions.
3. A gripper plate according to claim 2, wherein the inclination angle of
each of the leg portions is not equal.
4. A gripper plate according to claim 3, wherein the unequal inclination
angles of the leg portions are each selected so as to cause the leg
portions to substantially duplicate a thread pattern complimentary to that
of the threaded end portion of the rock bolt.
5. A gripper plate according to claim 4, wherein the free ends of the leg
portions are concavely curved.
6. A gripper plate according to claim 5, wherein the inclination angle of
the tab portions is substantially 90 degrees relative to the plane defined
by the base portion.
7. A gripper plate according to claim 6, wherein four leg portions are
positioned in equidistantly spaced relation around the perimeter of the
central opening.
8. A gripper plate according to claim 7, wherein four tab portions are
provided in equidistantly spaced relation around the perimeter of the
central opening.
9. A gripper plate according to claim 8, wherein the gripper plate is of
generally circular plan outline.
10. A gripper plate according to claim 9, wherein a raised boss of circular
plane outline is positioned on the lower surface of the base portion
adjacent the outer perimeter of said portion.
11. A gripper plate according to claim 10 constructed of hardened, spring
steel.
Description
FIELD OF THE INVENTION
The present invention relates to gripper plates, and more particularly to a
push-on gripper plates for securing a mesh screening means onto the
protruding end of rock bolts, such as are used in mine wall and roof
stabilization.
BACKGROUND OF THE INVENTION
It is well known in the mining and shoring arts to utilize rock bolts to
secure a wire mesh over the rock face of a mine roof or wall so as to
stabilize the rock face and reduce the risk of injury to mine personnel by
way of falling rock. Similar mesh screening means are sometimes used in
excavation and shoring operations where rock or shale faces may be
exposed. In both types of such operations, a suitably sized hole is
drilled into the rock or shale material generally perpendicular to its
face, and the rock bolt is inserted into the hole to a depth at which its
threaded free end protrudes beyond the rock face by several inches. The
rock bolts are retained in the drilled holes by any conventional means,
and such retention means, together with the rock bolts themselves are
well-known and are not part of the present invention.
After insertion of the rock bolt into a pre-drilled hole, a retention plate
having a centrally positioned hole is typically placed over the protruding
free end portion of the rock bolt and a conventional washer and nut are
threaded onto this free end to hold fast the retention plate against the
rock face and thereby stabilize the rock bolt within the rock material.
Conventional forms of retention plates are readily available for this
purpose, and examples thereof can be seen in U.S. Pat. Nos. 3,090,203
(Durget) and 4,740,111 (Gagnon), the teachings of which patents are hereby
incorporated by reference. Once the rock bolts are installed in this
manner, the wire mesh can be applied over the rock face and held
thereagainst by means of secondary fastening means. Such secondary
fastening means may be applied to the rock face independently of the rock
bolts, or more efficiently, by attachment to the protruding free end of
the rock bolts. The present invention is concerned with the provision of
an improved secondary attachment means of the latter type.
The mesh screening means used is typically a wire mesh screening means,
although other materials can be used. The size of the openings in the mesh
screening means is larger than the diameter of the rock bolts, so that the
rock bolts can pass freely therethrough. Of course, the mesh openings are
sufficiently small to prevent large pieces of the rock face from breaking
loose and passing through the installed mesh.
SUMMARY OF THE INVENTION
The present invention relates to a push-on gripper plate for use in
securement of a mesh screening means on the protruding, threaded, free end
of a rock bolt inserted into a rock face, wherein the gripper plate
comprises a generally planar base portion adapted to overlie the mesh
screening means. A central opening is provided in the base portion having
two or more leg portions positioned on the perimeter of the opening, the
leg portions being inclined downwardly, inwardly toward the centre of the
opening below the plane of the base portion. A plurality of tab portions
are also positioned on the perimeter of the opening in alternating
arrangement with the leg portions, the tab portions being inclined
downwardly, inwardly toward the centre of the opening below the plane
defined by the base portion. The inclination angle of the tab portions is
preferably steeper than the inclination angle of the leg portions. With
this arrangement, the leg portions are dimensioned and otherwise adapted
to frictionally engage therebetween the threaded end of the rock bolt to
hold the gripper plate on the end of the rock bolt over the mesh screening
means. Moreover, the tab portions are dimensioned and otherwise adapted to
together provide a gripping surface for overlying engagement by a socket
or other type of wrench, so as to allow the wrench to be used for pushing
the gripper plate on to the free end of the rock bolt, and/or for screw
tightening thereof during installation, should this be necessary.
The gripper plate described is simpler to manufacture and less expensive
than previously known gripper plates. It will be appreciated that both the
leg and the tab portions can be die punched in a single punch operation
from the material surrounding the perimeter of the opening. Not only does
this make the punching dies simpler and cheaper to construct, but there is
no material waste in the production of the gripper plate.
Other prior art gripper plates, such as that disclosed in U.S. Pat. No.
4,740,111 (Gagnon), have side flanges around the outer perimeter, which
side flanges require considerably more material to construct, at
substantially increased cost. Also, such side flanges, or other protruding
tabs spaced from the central opening make packaging, handling and shipping
of the gripper plates more difficult, as tight nesting of the prior art
plates is not easily achievable.
It should also be appreciated with the gripper plate of the present
invention, that the folding back of the tab portions away from the edge of
the central opening give a greater freedom of choice in the angling and
dimensioning of the leg portions of the gripper plate, which factors are
highly critical to the yield strength of the gripper plate. Moreover, such
freedom of choice allows the leg portions to be freely dimensioned and
angled to accommodate a wide range of rock bolt diameters and thread
patterns. In a preferred embodiment of gripper plate according to the
invention, each of the leg porions extending from the perimeter of the
central opening has a different inclination angle, such that each leg
portion contacts the rock bolt thread at a different angle. This
difference in contact angle can be tailored to a specific thread pattern,
so as to dramatically increase the gripping strength of the gripper plate,
to the extent that loads in excess of the failure loads of the screening
means can be achieved. As such, the gripper plate ceases to be the weakest
link in the support system, as has been the case with prior art gripper
plates. These and other advantages of the novel gripper plate disclosed
herein will become more apparent from the detailed description of a
preferred embodiment of the invention which follows immediately below.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Introduction to the Drawings
FIG. 1 of the drawings appended hereto is a schematic view illustrating
installation of a wire mesh screening means onto the end of a rock bolt
utilizing a gripper plate according to the invention;
FIG. 2 of the drawings is a perspective view of the gripper plate and rock
bolt of FIG. 1;
FIG. 3 of the drawings is a top plan view of the gripper plate of FIGS. 1
and 2; and,
FIG. 4 is a sectional view of the gripper plate of FIGS. 1, 2, and 3, taken
along line 4--4 of FIG. 3.
Referring now to the drawings, there will be seen a push-on gripper plate
10 for use in securement of a mesh screening means 12 on the protruding,
threaded, end portion 15 of a rock bolt 14 inserted into a rock face 16.
The rock bolt 14 is of well-known construction, and is inserted into a
drilled hole (not shown) in the rock face 16, so that the threaded portion
15 protrudes several inches beyond the rock face. After such insertion,
but prior to installing the gripper plate 10, a conventional retention
plate 30 is placed over the threaded portion 15 of the rock bolt 14,
followed by a conventional washer 32. A conventional nut 34 is then
tightened against the retention plate 30, so as to hold the retention
plate 30 against the rock face 16, and thereby anchor the rock bolt 14.
Once the rock bolt 14 is installed in this manner, a conventional wire
mesh screening means 12 is placed over the protruding threaded end portion
15 of the rock bolt 14, with the threaded end 14 passing through a hole in
the screening means 12. The gripper plate 10 is then pushed over the
threaded end portion 15, either by hand, or, if necessary, with the aid of
a socket or similar type of wrench (not shown) in a manner more fully
described below.
The gripper plate 10 comprises a generally planar base portion 18 adapted
to overlie the mesh screening means 12. A central opening 20 in the base
portion 18 has four leg portions 22 positioned on the perimeter of the
central opening 20, each of the leg portions being inclined, in use,
downwardly, inwardly toward the centre of the opening 20 above the plane
of the base portion, as best seen in FIG. 1. The inclination angle of the
leg portions 22 is nominally 45 degrees from the plane defined by the base
portion 18, but each of such leg portions may be several degrees greater
or less than 45 degrees. In fact, it is preferable that the inclination
angle of the four leg portions 22 not be equal, so as to enhance retention
of the gripper plate 10 on the screw threads of the threaded portion 15 of
the rock bolt 14. The exact inclination angle of each leg portion 22 can
be routinely calculated in respect of each leg portion 22, with specific
reference to the size of the central opening 20, the diameter of the
threaded end portion 15 and the dimensions and angling of the particular
thread pattern used on the end portion 15. The object of such calculations
is to angle the leg portions 22 to generally mimic the thread pattern of
the nut 34, (which thread pattern is complementary to that of the threaded
end portion 15) so as to maximize the axial load bearing characteristics
of the gripper plate 10, while at the same time allowing the gripper plate
109 to be pushed on to the protruding end 15 of the rock bolt 14 without
the absolute need of full threading. The free ends 38 of the leg portions
22 are preferably concavely curved (see especially FIG. 4) so as to more
firmly nest in engaged relation between the individual threads of the
threaded end portion 15 (see especially FIG. 2).
Four tab portions 28 are also positioned on the perimeter of the central
opening 20 in equidistantly spaced relation from one another, the tab
portions 28 being preferentially angled at substantially 90 degrees
relative to the plane defined by the base portion 18, so as to facilitate
their being frictionally engaged by the inside diameter of a socket wrench
for ease of installation. In such instance, the gripper plate 10 is simply
placed on the end of the socket wrench (not shown) with the four tab
portions inserted into the socket wrench. Then, the gripper plate is
pushed over the threaded free end 15 of the rock bolt 14, until the base
portion 18 contacts the nut 34 or the wire screening means 12, whereupon
final tightening of the gripper plate 10 by means of the socket wrench can
be achieved. Of course, such rotary tightening can be utilized at any
point of travel of the gripper plate 10 along the threaded end portion 15,
should the leg portions 22 bind with the threading on the rock bolt 14.
Moreover, removal of the gripper plate 10 through use of a socket or
similar wrench is facilitated by the presence of the tab portions 28.
As illustrated, it is preferred to have four leg portions 22 and four tab
portions 28 positioned on the central opening in alternating fashion, each
of the leg 22 and tab 28 portions being equidistantly spaced around said
opening. With the tab portions 28 pulled downwardly to an inclination
angle of substantially 90 degrees, this arrangement provides for maximum
flexibility in design of the leg portions 22.
A raised boss 36 of circular plan outline is preferably provided on the
lower surface (as seen in FIG. 1) of the base portion 18 of the gripper
plate 10 adjacent to the outer perimeter of the base portion 18. This boss
36 adds riqidity to the base portion 18.
During installation, the friction plate 10 is pushed on to the rock bolt 14
to secure the mesh screening means 18 between a standard retention plate
30 and the rock face 16, as shown in FIG. 1. A socket or similar wrench
(not shown) may be used in the installation to assist in pushing on or
tightening of the gripper plate, but this is not necessary in most
applications. The installation operation is simpler than with prior art
gripper plates, and may be done by hand without the use of jacklegs or
stoppers in a minimum period of time.
Preliminary pull tests were done on steel gripper plates as illustrated
constructed of C1050 spring steel, hardened and tempered to a Rockwell "C"
scale hardness of RC 32 to 40, with an average hardness of RC 38. The
thickness of the plate metal was 0.060 inches, and the outside diameter
was 5 inches. The threaded section of a 5/8" O.D. rock bolt was inserted
into the tensioner and the gripper plate was installed on the rock bolt as
previously described. Loads were then applied to the gripper plates in
three different modes as follows: a) directly to the hub of the plates; b)
as an annulus 2" from the hub of the plates; and, c) as an annulus 4" from
the hub of the plate. In the hub loading mode a), average loading at
failure was 3.75 tons. In the 2" annulus loading mode b), average loading
at failure was 2.5 tons, and in the 4" annulus loading, the average
loading at failure was 2.2 tons.
Similar test conducted on the gripper plates using a 3/4" O.D. rock bolt
resulted in average failure loads of 2.8 tons.
Failure during testing was gradual, on a thread by thread basis, with the
gripper plates tending to slide down the rock bolt a thread at a time.
Unlike the prior art gripper plates, including the plate disclosed in U.S.
Pat. No. 4,740,111, the threads of the rock bolts were not damaged after
failure. Moreover, the gripper plates tested could, after failure, still
be re-installed on the rock bolt by hand, and after such re-installation
still carried an average residual load of almost 1 ton for the 5/8 inch
bolts and 1 ton for the 3/4 inch bolts. These factors combine to provide a
better chance than with known gripper plates to contain the mesh screening
means following an instantaneous loading situation. Moreover, these tests
indicate consistent failure loads in excess of the failure loads of most
mesh screening means used in mining operations, thus confirming that the
subject gripper plates are not the weak link in the supplementary support
system described herein.
Although this invention has been disclosed with reference to a particular
preferred embodiment as shown and described, it is to be understood that
it is not to be limited to such embodiment and that other alternatives are
envisaged within the scope of the following claims.
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